1. Field of the Invention
The present invention relates to stators of vehicle alternators driven by internal combustion engines and, more particularly, to a stator of a vehicle alternator installed on vehicles such as passenger cars, trucks, or boats and ships.
2. Description of the Related Art
Attempts have heretofore been made to provide vehicle alternators having stator windings of first and second types. The stator winding of the first type includes a continuous wire. The stator winding of the second type includes a segment, made of an electrical conductor preliminarily bent in a hairpin shape (such a bent portion will be hereinafter referred to as a turning portion), which is inserted to slots of the stator after which ends of the segment are joined to each other (see, for instance, Japanese Unexamined Patent Application Publication No. 346448, on pages 3 to 8 and FIGS. 1 to 19: Patent Document I).
With such a structure, the stator winding has coil end groups, axially protruding from axial end faces of the stator core, in one of which a turning portion of a large segment disposed in inner and outer layers of slots is arranged so as to surround a turning portion of a small segment disposed in middles layers of the slots. Since the stator winding is configured such that the turning portion of the large segment surrounds the turning portion of the small segment, the small segment has a less surface area that directly gets cooling wind with the resultant deterioration in cooling efficiency. Therefore, this results in increased heat development in peripherals parts of the turning portion of the small segment, causing degraded heat radiating property of the small segment.
To take measures against such deterioration in cooling efficiency, an attempt has been made to provide a winding structure composed of large and small segments whose turning portions are dislocated from each other in a circumferential direction of a stator core to provide improved cooling efficiency (see, for instance, Japanese Patent No. 3407676 on pages 3 to 5 and FIGS. 1 to 7: Patent Document II).
With the winding structure disclosed in Patent Document II, since a height of a coil end of the turning portion of the large segment depends on a height of a coil end of the turning portion of the small segment, a difficulty is encountered in reducing a height of the turning portion. Therefore, an issue has arisen with a difficulty of shortening a length of a winding to decrease a resistance value of the winding for the purpose of suppressing an increase in heat development and increasing an output of the alternator. In addition, resistance in airflow around a frame surrounding the coil end cannot be decreased and in maintaining a physical constitution of the vehicle alternator, an issue arises with a difficulty of increasing the flow rate of cooling wind.